Pekka Haavisto, head of the U.N. team that checked some of the sites targeted most often by NATO, urged the West to act "quite rapidly to avoid any future damage to human lives and to the environment."
The U.N. team found some "hot spots" of pollution affected by the NATO bombing - particularly in the heavily targeted Serb towns of Pancevo and Kragujevac, where mercury, asbestos and other hazardous substances were found spilled into the environment.
"I strongly would recommend that this kind of action should be taken as part of humanitarian action to the area despite all the political problems that might be connected to the reconstruction," Haavisto told reporters.
The United States and its allies have refused to give any reconstruction aid to Yugoslavia while President Slobodan Milosevic is in power, saying they will provide only humanitarian assistance.
The U.N. Environmental Program team carried out a nine-day investigation at some of the sites targeted most often by NATO during its 78-day campaign. Yugoslav officials have said strikes on factories and other targets caused widespread environmental damage and health hazards.
Haavisto suggested that the damage was not as severe as the Serbs had claimed. "There are some hot spots where immediate action has to take place but there is not a countrywide catastrophe. This is our first judgment," he said.
Many of the environmental problems predated the NATO bombing, although airstrikes may have worsened some of them, he said.
The U.N. team visited factories and oil refineries hit by NATO throughout Yugoslavia during the campaign, which began March 24. Haavisto said the discovery of the hazardous materials in Pancevo, northwest of the Yugoslav capital Belgrade, and Kragujevac in central Serbia was "very worrying."
He said the initial findings did not show an increased level of radioactivity from any bombs containing depleted uranium as was feared. But he noted there might be other consequences of such bombing that still need to be examined.
The team's final report, expected by early September, will go to U.N. Secretary-General Kofi Annan, who will decide on possible corrective measures.